Downward movement of dolomite, kieserite or a mixture of CaCO3 and kieserite through the upper layers of an acid forest soil

Liming and fertilization are important tools for improving the chemical status of acid, base poor forest soils. The downward movement of dolomite, kieserite and a mixture of CaCO3 and kieserite was investigated by monitoring the leachates and exchangeable cation composition from single and combined horizon columns, reconstructed from an acid brown forest soil profile (0-15 cm). Upon entering the soil, Mg ions from kieserite displaced base cations and acidity (H and Al ions) from exchange sites, which subsequently moved down with the mobile SO42- anions. Total leaching during the initial SO42- pulse was similar with the CaCO3 + kieserite mixture. Compared to the single kieserite treatment, the joint application of CaCO3 greatly increased the proportion of Ca in the leachates from all horizons. It also decreased the leaching of acidity from the surface Oe horizon and prevented pH from dropping under this layer. With both treatments, the redistribution of magnesium with SO42- anions resulted in a rapid increase in exchangeable Mg contents throughout the studied columns. Due to the important charge increase in the Oe horizon and to kinetic restraints imposed on dissolution, downward movement of Ca and Mg ions from dolomite was very limited. Mg was however much more mobile than Ca. In the CaCO3 + kieserite and dolomite treatments, the migration of alkalinity and base cations with time was associated with a decrease in exchangeable acidity and an increase in ECEC in the two upper soil layers. By the end of the monitoring period, overall net Mg retention in the 0-15 cm columns increased in the order kieserite < CaCO3 + kieserite << dolomite with respectively 20, 35 and 85% of cumulated inputs remaining in the columns. The corresponding net Ca retention amounted to 82 and 96% of cumulated inputs for the CaCO3 + kieserite and dolomite treatments, respectively. Results from this study complement those obtained in the field by clearly demonstrating the mechanisms involved in the downward movement of some fertilizers commonly used to increase the base saturation of acid forest soils.